diff --git a/cpp2rust/converter/converter.cpp b/cpp2rust/converter/converter.cpp
index 1b3ed81e..5cad686c 100644
--- a/cpp2rust/converter/converter.cpp
+++ b/cpp2rust/converter/converter.cpp
@@ -552,7 +552,8 @@ static bool recordDerivesCopy(const clang::RecordDecl *decl) {
   for (auto f : decl->fields()) {
     // Records that contain std::vector, std::array, std::string or anything
     // that is translated to Vec<>, do not derive Copy
-    if (Mapper::Map(f->getType()).starts_with("Vec<")) {
+    auto mapped = Mapper::Map(f->getType());
+    if (mapped.starts_with("Vec<")) {
       return false;
     }
 
@@ -560,7 +561,7 @@ static bool recordDerivesCopy(const clang::RecordDecl *decl) {
       return false;
     }
 
-    if (Mapper::Map(f->getType()).starts_with("BTreeMap<")) {
+    if (mapped.starts_with("BTreeMap<")) {
       return false;
     }
 
@@ -653,7 +654,7 @@ void Converter::EmitRustStruct(clang::RecordDecl *decl) {
     auto struct_name = GetRecordName(cxx);
 
     ConvertCXXMethodDecls(
-        cxx, std::string(keyword::kImpl) + ' ' + struct_name,
+        cxx, std::format("{} {}", keyword::kImpl, struct_name),
         [](const auto *method) {
           return !method->isImplicit() &&
                  !(method->getDefinition() &&
@@ -701,7 +702,7 @@ bool Converter::VisitCXXRecordDecl(clang::CXXRecordDecl *decl) {
   if (decl->isStruct() || decl->isClass()) {
     for (auto c : GetTemplateInstantiatedCtors(decl)) {
       if (!decl_ids_.contains(GetID(c))) {
-        StrCat(std::string(keyword::kImpl) + ' ' + GetRecordName(decl));
+        StrCat(keyword::kImpl, GetRecordName(decl));
         PushBrace brace(*this);
         VisitCXXMethodDecl(c);
       }
@@ -1875,7 +1876,7 @@ bool Converter::VisitBinaryOperator(clang::BinaryOperator *expr) {
   auto *rhs = expr->getRHS();
   auto lhs_type = lhs->getType();
   auto rhs_type = rhs->getType();
-  std::string opcode_as_string = expr->getOpcodeStr().str();
+  std::string_view opcode_as_string = expr->getOpcodeStr();
 
   if (auto *cmpd_assign_op =
           llvm::dyn_cast<clang::CompoundAssignOperator>(expr);
@@ -1901,7 +1902,9 @@ bool Converter::VisitBinaryOperator(clang::BinaryOperator *expr) {
         Convert(lhs);
         ConvertCast(computation_result_type);
       }
-      StrCat(std::regex_replace(opcode_as_string, std::regex("="), ""));
+      std::string op(opcode_as_string);
+      op.erase(std::remove(op.begin(), op.end(), '='), op.end());
+      StrCat(op);
       Convert(rhs);
     }
     if (lhs_type->isBooleanType()) {
@@ -2206,7 +2209,7 @@ bool Converter::VisitParenExpr(clang::ParenExpr *expr) {
 bool Converter::ConvertCXXOperatorCallExpr(clang::CXXOperatorCallExpr *expr) {
   switch (expr->getOperator()) {
   case clang::OverloadedOperatorKind::OO_Equal:
-    ConvertAssignment(expr->getArg(0), expr->getArg(1), token::kAssign);
+    ConvertAssignment(expr->getArg(0), expr->getArg(1), "=");
     break;
   case clang::OverloadedOperatorKind::OO_Star:
   case clang::OverloadedOperatorKind::OO_Arrow:
@@ -2785,40 +2788,43 @@ std::string Converter::GetDefaultAsString(clang::QualType qual_type) {
   } else if (auto *array_type =
                  clang::dyn_cast<clang::IncompleteArrayType>(qual_type)) {
     return GetDefaultAsString(array_type->getElementType());
-  } else if (Mapper::ToString(qual_type) == "struct std::pair") {
-    auto template_args = *GetTemplateArgs(qual_type);
-    auto first_type = template_args[0].getAsType();
-    auto second_type = template_args[1].getAsType();
-    return std::format("({}, {})", GetDefaultAsString(first_type),
-                       GetDefaultAsString(second_type));
-  } else if (Mapper::ToString(qual_type).contains("std::array")) {
-    assert(GetTemplateArgs(qual_type).has_value());
-    auto template_args = *GetTemplateArgs(qual_type);
-    assert(template_args.size() == 2);
-    auto array_size = template_args[1];
-    unsigned size = 0;
-    switch (array_size.getKind()) {
-    case clang::TemplateArgument::Expression: {
-      auto array_size_expr = array_size.getAsExpr();
-      assert(array_size_expr && !array_size_expr->isValueDependent());
-      clang::Expr::EvalResult result;
-      ENSURE(array_size_expr->EvaluateAsInt(result, ctx_));
-      size = result.Val.getInt().getZExtValue();
-      break;
-    }
-    case clang::TemplateArgument::Integral: {
-      size = array_size.getAsIntegral().getZExtValue();
-      break;
-    }
-    default:
-      assert(0 && "Unsupported array size kind");
-      break;
-    }
-    return std::format(
-        "std::array::from_fn::<_, {}, _>(|_| Default::default()).to_vec()",
-        size);
   } else {
-    return GetDefaultAsStringFallback(qual_type);
+    auto qual_type_str = Mapper::ToString(qual_type);
+    if (qual_type_str == "struct std::pair") {
+      auto template_args = *GetTemplateArgs(qual_type);
+      auto first_type = template_args[0].getAsType();
+      auto second_type = template_args[1].getAsType();
+      return std::format("({}, {})", GetDefaultAsString(first_type),
+                         GetDefaultAsString(second_type));
+    } else if (qual_type_str.contains("std::array")) {
+      assert(GetTemplateArgs(qual_type).has_value());
+      auto template_args = *GetTemplateArgs(qual_type);
+      assert(template_args.size() == 2);
+      auto array_size = template_args[1];
+      unsigned size = 0;
+      switch (array_size.getKind()) {
+      case clang::TemplateArgument::Expression: {
+        auto array_size_expr = array_size.getAsExpr();
+        assert(array_size_expr && !array_size_expr->isValueDependent());
+        clang::Expr::EvalResult result;
+        ENSURE(array_size_expr->EvaluateAsInt(result, ctx_));
+        size = result.Val.getInt().getZExtValue();
+        break;
+      }
+      case clang::TemplateArgument::Integral: {
+        size = array_size.getAsIntegral().getZExtValue();
+        break;
+      }
+      default:
+        assert(0 && "Unsupported array size kind");
+        break;
+      }
+      return std::format(
+          "std::array::from_fn::<_, {}, _>(|_| Default::default()).to_vec()",
+          size);
+    } else {
+      return GetDefaultAsStringFallback(qual_type);
+    }
   }
 }
 
diff --git a/cpp2rust/converter/converter_lib.cpp b/cpp2rust/converter/converter_lib.cpp
index 4d561fcc..88a4c9b1 100644
--- a/cpp2rust/converter/converter_lib.cpp
+++ b/cpp2rust/converter/converter_lib.cpp
@@ -268,11 +268,10 @@ std::string GetFileName(const clang::Decl *decl) {
   const auto &ctx = decl->getASTContext();
   const auto full_location = ctx.getFullLoc(decl->getBeginLoc());
   const auto file_name = ctx.getSourceManager().getFilename(full_location);
-  const auto file_name_as_string = file_name.str();
-  const std::filesystem::path file_path(file_name_as_string);
+  const std::filesystem::path file_path(file_name.begin(), file_name.end());
   return std::filesystem::exists(file_path)
              ? std::filesystem::canonical(file_path).string()
-             : file_name_as_string;
+             : file_path.string();
 }
 
 unsigned GetLineNumber(const clang::Decl *decl) {
diff --git a/cpp2rust/converter/lex.h b/cpp2rust/converter/lex.h
index db69958d..cf7da5db 100644
--- a/cpp2rust/converter/lex.h
+++ b/cpp2rust/converter/lex.h
@@ -13,7 +13,7 @@ inline constexpr const char *kSemiColon = ";\n";
 inline constexpr char kComma = ',';
 inline constexpr char kColon = ':';
 inline constexpr const char *kDoubleColon = "::";
-inline constexpr const char *kAssign = "=";
+inline constexpr char kAssign = '=';
 inline constexpr char kOpenParen = '(';
 inline constexpr char kCloseParen = ')';
 inline constexpr char kDot = '.';
diff --git a/cpp2rust/converter/mapper.cpp b/cpp2rust/converter/mapper.cpp
index 425cf805..9193b32f 100644
--- a/cpp2rust/converter/mapper.cpp
+++ b/cpp2rust/converter/mapper.cpp
@@ -732,7 +732,7 @@ std::string ToString(clang::QualType qual_type) {
   std::string type;
   llvm::raw_string_ostream os(type);
   normalizeQualType(qual_type).print(os, getPrintPolicy());
-  return normalizeTranslationRule(type);
+  return normalizeTranslationRule(std::move(type));
 }
 
 std::string ToString(const clang::NamedDecl *decl) {
@@ -753,7 +753,7 @@ std::string ToString(const clang::NamedDecl *decl) {
 
   if (!func_decl) {
     decl->printQualifiedName(os, getPrintPolicy());
-    return normalizeTranslationRule(out);
+    return normalizeTranslationRule(std::move(out));
   }
 
   os << ToString(func_decl->getReturnType()) << " ";
@@ -798,7 +798,7 @@ std::string ToString(const clang::NamedDecl *decl) {
     }
   }
 
-  return normalizeTranslationRule(os.str());
+  return normalizeTranslationRule(std::move(out));
 }
 
 std::string ToString(const clang::Expr *expr) {
diff --git a/cpp2rust/converter/models/converter_refcount.cpp b/cpp2rust/converter/models/converter_refcount.cpp
index 0442ae75..f19a7d8a 100644
--- a/cpp2rust/converter/models/converter_refcount.cpp
+++ b/cpp2rust/converter/models/converter_refcount.cpp
@@ -6,7 +6,6 @@
 #include <clang/Basic/OperatorKinds.h>
 
 #include <format>
-#include <regex>
 
 #include "compiler.h"
 #include "converter/converter_lib.h"
@@ -1144,7 +1143,7 @@ bool ConverterRefCount::VisitBinaryOperator(clang::BinaryOperator *expr) {
   auto *rhs = expr->getRHS();
   auto lhs_type = lhs->getType();
   auto rhs_type = rhs->getType();
-  std::string opcode_as_string = expr->getOpcodeStr().str();
+  std::string_view opcode_as_string = expr->getOpcodeStr();
 
   if (auto *assign = llvm::dyn_cast<clang::CompoundAssignOperator>(expr);
       assign && lhs_type != assign->getComputationResultType()) {
@@ -1165,7 +1164,9 @@ bool ConverterRefCount::VisitBinaryOperator(clang::BinaryOperator *expr) {
         StrCat(ConvertRValue(lhs));
         ConvertCast(computation_result_type);
       }
-      StrCat(std::regex_replace(opcode_as_string, std::regex("="), ""));
+      std::string op(opcode_as_string);
+      op.erase(std::remove(op.begin(), op.end(), '='), op.end());
+      StrCat(op);
       Convert(rhs);
     }
     if (lhs_type->isBooleanType()) {
@@ -1805,7 +1806,7 @@ bool ConverterRefCount::ConvertCXXOperatorCallExpr(
     clang::CXXOperatorCallExpr *expr) {
   switch (expr->getOperator()) {
   case clang::OverloadedOperatorKind::OO_Equal:
-    ConvertAssignment(expr->getArg(0), expr->getArg(1), token::kAssign);
+    ConvertAssignment(expr->getArg(0), expr->getArg(1), "=");
     break;
 
   case clang::OverloadedOperatorKind::OO_Arrow: